1. Field of the Invention
The present invention relates to a piping system connected to equipment in a petrochemical plant or a power plant. The equipment is a rotary machine such as an expander of a fluidized catalytic cracker (FCC) or to a high-temperature reactor, and the like in which the allowable value of a load applied from a pipe arrangement is small.
2. Description of the Related Art
Since the expander of the FCC has a precise rotational mechanism, any excessive force or moment must be prevented from being applied to an equipment of this type. Hence, in a metal piping system connected into an equipment nozzle installed in such an equipment, measures are taken to reduce loads on the nozzle.
One of such measures taken conventionally is installing several tied expansion joints installed in the piping system to absorb displacement caused by thermal displacement of the equipment nozzle and thermal expansion of the pipe during facility running. As the expansion joint, a bellows type expansion joint including a bellows (refer to Japanese Industrial Standard (JIS) B 2352) is generally known. Table 1 of JIS B 2352 shows several types of bellows type expansion joints. Applying a simplest untied bellows type expansion joint among them to connect the pipes to each other enables absorption of axial displacement, axial-perpendicular displacement, and angular displacement of the pipe in an arbitrary plane excluding a twist. As a result, loads on the nozzle can be reduced by converting large force due to bending of pipe into small force due to bending of bellows.
In a joint of this type, however, a force (hereinafter, internal-pressure thrust) generated by internal pressure in the bellows in a direction on separating the pipes from each other (or direction for attracting each other) is applied to the equipment nozzle. This makes it difficult to apply the simple untied bellows type expansion joint when a pipe bore or the internal pressure becomes larger. In such a case, a tied bellows type expansion joint is used, which includes a mechanism of restricting axial expansion of the bellows no to transmit the internal-pressure thrust to the outside of the bellows. Well-known types of tied bellows type expansion joints include a hinge type expansion joint that absorbs only angular displacement in one plane by using a hinge at pipe ends connected via the bellows, a gimbal type expansion joint that absorbs not only the angular displacement in one plane but also angular displacement in an arbitrary plane, and a universal expansion joint that absorbs axial-perpendicular displacement in the arbitrary plane (refer to JP10-141565A).
Where the piping system moves vertically due to thermal expansion of each piping member, a special pipe support device to support piping weight with following the vertical movement is necessary. For this purpose, the piping system is installed in a lifted state by using spring hanger supports such as variable spring hangers or constant spring hangers that has a mechanism to reduce load variation by the movement.
As a method for using the bellows type expansion joint to absorb the axial displacement without transmitting the internal-pressure thrust to the outside of the bellows type expansion joint, a bellows type expansion joint of pressure balanced type is used, which additionally includes a bellows to cancel the internal-pressure thrust and tie rods disposed to permit the axial displacement in a state of keeping the balance (refer to FIG. 8 of JP10-141565A or FIGURES of U.S. Pat. No. 4,265,472).
As described above, in the conventional piping system that includes several tied bellows type expansion joints, the loads applied on the equipment nozzle can be reduced. However, this load reduction measure is becoming insufficient due to recent trend toward larger capacity plant.
When a pipe bore increases as the plant is enlarged, the internal-pressure thrust applied at bellows becomes larger, and the spring constant of the bellows itself increases. The pipe also becomes longer, and hence displacement to be absorbed is enlarged. A frictional force at a sliding portion such as the hinge or the gimbal increases, causing an increase in loads on the equipment nozzle. The spring hanger supports also have friction at sliding portion and spring itself, and reaction force generates during movement. This force is called as load for initial movement and it becomes approximately 5% of supporting load. Thus, an influence of the force in the spring hanger supports on the equipment nozzle can no longer be negligible. For example, pipe weight is 11 tons per meter in the case of a stainless-steel pipe having a diameter of φ3500 millimeters and a thickness of 135 millimeters. When 14 meters of pipe is supported by spring hanger supports on the equipment nozzle, total pipe weight is 150 tons and the load for initial movement reaches about 7.5 tons. As a result, this load becomes predominant, exceeding the allowable value of a load for the equipment nozzle.
In order to prevent application of various loads including the internal-pressure thrust, the spring reaction force, and the frictional force of the piping system, and the operation resistance of the hanger support on the equipment nozzle, a method for installing a bellows type expansion joint of pressure balanced type between the equipment nozzle and the piping member and setting a fixed point (anchor) as close as possible to the bellows of the piping member to fix the piping system, has been considered on a conceptual basis. This anchor prevent any piping load, friction and reaction force being transmitted to the equipment nozzle side from another side of the anchor by rigidly supporting the piping However, in the conventional art, this method has been difficult for the following reasons.
Under such conditions, an internal-pressure thrust and a spring reaction force due to displacement of the bellows are applied to the equipment nozzle. The internal-pressure thrust can be absorbed by employing the above-mentioned bellows type expansion joint of pressure balanced type. However, when the piping member close to the bellows is fixed, all axial thermal expansion at the equipment nozzle must be absorbed by compression displacement of the bellows. When the bellows type expansion joint of pressure balanced type is employed, the pipe bore is enlarged to increase the spring constant of the single bellows, and the influence of an additional pressure balanced type bellows increases the spring constant more. As a result, the spring reaction force increases, and the loads on the equipment nozzle exceed the allowable value, making it impractical to set an anchor in the piping member close to the bellows within the scope of conventional art. Therefore, there is an urgent need to achieve a method for setting an anchor in the piping member close to the bellows by developing a pressure balanced type expansion joint system with a novel technology. That is to balance spring reaction force of main bellows by displacement at equipment nozzle with that of balanced bellows by thermal displacement at piping piece in the expansion joint system.